As the process control of manufacturing has improved, industry has sought efficient techniques for uniquely identifying products. This call for identification not only is concerned with the application of sequential, alpha-numeric strings to completed products, but also has application to component pans of fabrications such as automobiles and piece pans which are progressing through an industrial process.
The generation of computer selected character strings on piece parts which are of sufficient permanence and quality with adequate marking rapidity so as to permit the use of the marking process concurrently during production procedures has posed an elusive goal to investigators. A successful procedure and apparatus for marking unique computer generated character sequences upon the surfaces of somewhat maleable materials such as metals and plastics has been described in 1985 in U.S. Pat. No. 4,506,999 by Robertson, entitled "Program Controlled Pin Matrix Embossing Apparatus". This patent describes a computer driven dot matrix marking technique which has been successfully introduced in the marketplace under the trade designation "PINSTAMP". The marking approach employs a series of tool steel punches which are uniquely driven using a pneumatic floating impact concept to generate man readable and/or machine readable dot characters or codes. The marking technique enjoys the advantage of providing characters of good legibility as well as permanence.
Robertson, et al. in U.S. Pat. No. 4,808,018, entitled "Marking Apparatus with Matrix Defining Locus of Movement", issued Feb. 28, 1989, describes a dot matrix character impact marking apparatus which is capable of forming messages or arrays of characters within a very confined region. With this device, a linear array of marker pins is moved by a carriage in a manner defining an undulating locus of movement. During this movement, computer evoked alpha-numeric character strings and the like are generated.
Robertson, et al. in U.S. Pat. No. 5,015,106, issued May 14, 1991, and entitled "Marking Apparatus with Multiple Line Capability" describes a dot matrix character impact marking apparatus which achieves a multiple line capability wherein a carriage component carrying one or more marker pin cartridges moves within a singular plane locus of movement. This multiple line capability has permitted a broad variety of line configurations in widely spaced positions at a workplace. The device further employs a retrace method in generating a locus of marking movement somewhat similar to the formation of a raster in conjunction with television systems.
In U.S. Pat. No. 5,316,397 by Robertson, et al., entitled "Marking Apparatus with Multiple Marking Modes", issued May 31, 1994, a highly versatile marking apparatus and system is described having a flexibility for marking to provide characters in multiple formation modes including the marking of continuous characters as well as dot matrix characters, again utilizing a marker pin based approach.
Single pin marking also has been introduced to industry wherein a pneumatically driven marking pin is maneuvered under a robotic form of control in correspondence with appropriate hardware and software. Such devices are sold, for example, as the Model TMP 6000 marketed by Telesis Marking Systems, Inc. of Chillicothe, Ohio. This software and hardware integrated system provides the capability of maneuvering a marking device along a locus of movement for programmably defining characters and the like within a string.
As these capabilities for computer driven marking of metals and plastics have been introduced and enhanced, industry now has considered the desirability for practical marking systems which can permanently record coded and usually serialized character strings on the surfaces of brittle materials such as glass. The characters of these strings must be adequately small, thus calling for the formation of thin character forming lines. Under consideration by industry are requirements for marking vehicle identification numbers (VIN) on glass auto parts for security and source tracking purposes. Also contemplated is the marking of glass envelopes, for example cathode ray tubes and the like, where it is desirable to record mold source, time, and date data. Such marking, for example with sequential alpha-numeric strings, must be of a level of quality adequate to avoid detracting from the aesthetic properties of the product and, at the same time, achieve the desired permanence developed by indentation formed markings heretofore made in somewhat maleable materials such as metals and plastics. In the latter regard, the marks must be capable of surviving high annealing temperatures while remaining highly visible for machine reading. Where brittle materials such as glass are marked using reciprocating pins or the like, the resultant marks are aesthetically undesirable both from the standpoints of sight and the presence of a "gritty" tactile effect or feel. Of more import, such marking procedures are prone to generate stress risers which tend to weaken glass products, inasmuch as they may become sources of crack propagation.
Preferably, brittle glass products are marked with procedures achieving a subtle "frosting" effect. For the most part, this has been achieved by applying etchants such as hydrofluoric acid or abrasive blast through masks or stencils or by the application of small abrasive grinding wheels, both procedures being overly time consuming and labor intensive. For example, where serialized VIN numbers are to be marked, a separate stencil is required for each application. Following such application, cleaning procedures are required resulting in techniques which are ill suited for mass production procedures.